Studies were undertaken to investigate the immunologic responsiveness of normal individuals and patients with immunologic disorders as well as experimental animals serving as models of human diseases. BIBLIOGRAPHIC REFERENCES: Nelson, D.L., Strober, W., Abelson, L.D., Bundy, B.M. and Mann, D.L.: Distribution of alloantigens on human Fc receptor-bearing lymphocytes: The presence of B-cell alloantigens on sIg-positive but not sIg-negative lymphocytes. J. Immunol. 118:943-946, 1977. Nelson, D.L., Bundy, B.M. and Strober, W.: Spontaneous cytotoxicity by human peripheral blood lymphocytes. In Lucas, D.O. (ed.): Regulatory Mechanisms in Lymphocyte Activation: Proceedings of the Eleventh Leukocyte Culture Conference, Academic Press, New York. In press, 1977.